试图从 mysql 中检索文本和 blob 到 jtable

Question

所以我试图以一种很好的方式从 jtable 中的数据库中检索文本和 blob（图像）。出于某种原因，每当我尝试检索 blob 时，我都会得到：

java.io.ByteArrayInputStream@1cb63183

在每隔一列中，尽管我已经指定 blob 在 8 号！

这里是截图：

http://s24.postimg.org/t71o3izlh/Screen_Shot_2016_01_28_at_1_26_55_PM.png

这是我的代码

sql = "SELECT * FROM Products";  

ResultSet rs = stmt.executeQuery(sql);

  ResultSetMetaData rsmd = rs.getMetaData();
 // getting the columns number
  int columnsNumber = rsmd.getColumnCount();

// setting a vector with columns number
Vector columns = new Vector(columnsNumber);


 // adding column names
for(int i=1; i<=columnsNumber; i++)
columns.add(rsmd.getColumnName(i));

// setting a vector with row data
Vector rowdata = new Vector();
Vector row;
JTable table = new JTable(rowdata, columns);

while(rs.next())
{

 row = new Vector(columnsNumber);

    for(int i=1; i<=columnsNumber; i++)
   {
    // adding the rows in "row vector"
    InputStream binaryStream = rs.getBinaryStream(i);
    row.add(rs.getString(i));
    row.add(rs.getBinaryStream(8));

}
// adding the rows in the database
rowdata.add(row);
}

有人可以向我解释为什么这种方法不起作用吗？

顺便说一句，如果我删除了这一行：

 row.add(rs.getBinaryStream(8));

获取 java.io.ByteArrayInputSteam 的问题将消失，但是，我只会获取图像的文本表示。

它实际上不是重复的，因为我试图根据我有多少行（文本和图像）将其添加到特定列中。所以它是动态完成的，与 "possible duplicate"

不同，sql 同时具有图像和文本

提前致谢！

Answer 1

所以，您似乎遇到了一系列复杂的问题。让我们从这里开始，从数据库加载数据...

while(rs.next())
    {
        row = new Vector(columnsNumber);

        for(int i=1; i<=columnsNumber; i++)
        {
            // adding the rows in "row vector"
            InputStream binaryStream = rs.getBinaryStream(i);
            row.add(rs.getString(i));
            row.add(rs.getBinaryStream(8));
        }
        // adding the rows in the database
        rowdata.add(row);
    }

因此，对于 ResultSet 中的每一行，您查看列，但是，对于每一列，您添加 String 值和最后一列的 blob，因此 blob 将添加 6 次（根据您的屏幕截图）。显然，这不是您想要的，也是您在其他所有列中获得 java.io.ByteArrayInputStream@1cb63183 的原因。

相反，您想遍历 1-columnsNumbers - 1 列，因为我们不想要最后一列，并将图像添加到最后一列，可能类似于...

while(rs.next())
{
    row = new Vector(columnsNumber);

    for(int i=1; i < columnsNumber; i++)
    {
        // adding the rows in "row vector"
        InputStream binaryStream = rs.getBinaryStream(i);
        row.add(rs.getString(i));
    }
    row.add(rs.getBinaryStream(8));
    // adding the rows in the database
    rowdata.add(row);
}

下一个问题...

它仍然在最后一列打印 java.io.ByteArrayInputStream@1cb63183！？

这只是因为您添加到 row Vector 的所有内容都是表示数据库中二进制数据的二进制流，JTable 无法呈现它。您应该首先查看 Concepts: Editors and Renderers and Using Custom Renderers，了解有关如何自定义这些组件的渲染的更多详细信息

首先，我们需要将二进制数据转换为我们可以使用的图像格式

row.add(ImageIO.read(rs.getBinaryStream(8)));

并使用类似于 Rendering BufferedImage in JTable cell

中概述的内容

或

row.add(new ImageIcon(ImageIO.read(rs.getBinaryStream(8))));

应该允许 "default" TableCellRenderer 渲染它

可运行示例...

警告：这个例子有点长，因为我必须构建数据库并填充它。为简单起见，它使用独立的 H2 Database engine，但应该可以转换为大多数其他数据库。该示例还使用了 blob 的列类型，这是故意的，因为它提高了数据库引擎的性能。

在使用 DefaultTableModel 时让图像显示在 JTable 中的问题是，DefaultTableModel returns Object.class 来自 TableModel#getColumnClass 方法

甚至 DefaultTableModel 文档也记录了这一点...

Warning: DefaultTableModel returns a column class of Object. When DefaultTableModel is used with a TableRowSorter this will result in extensive use of toString, which for non-String data types is expensive. If you use DefaultTableModel with a TableRowSorter you are strongly encouraged to override getColumnClass to return the appropriate type.

我通过自定义 DefaultTableModel 我从 TestPane#makeTableModel...

返回来克服了这个问题

DefaultTableModel model = new DefaultTableModel(new String[]{"Name", "Image"}, 0) {
    @Override
    public Class<?> getColumnClass(int columnIndex) {
        return columnIndex == 1 ? Icon.class : super.getColumnClass(columnIndex);
    }
};

这允许 JTable 使用正确的 TableCellRenderer

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.imageio.ImageIO;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.table.DefaultTableModel;

public class Main {

    public static void main(String[] args) {
        try {
            Class.forName("org.h2.Driver");
            makeDatabase();
            populateDatabase();
            new Main();
        } catch (ClassNotFoundException | SQLException | IOException exp) {
            exp.printStackTrace();
        }
    }

    protected static Connection makeConnection() throws SQLException {
        String path = "jdbc:h2:./TestDatabase";
        return DriverManager.getConnection(path, "sa", "");
    }

    protected static void makeDatabase() throws SQLException {
        String cmd = "create table if not exists fruits ("
                + "key BIGINT IDENTITY, "
                + "name varchar(128), "
                + "image longblob)";
        try (Connection con = makeConnection()) {
            try (PreparedStatement stmt = con.prepareStatement(cmd)) {
                System.out.println("> Make fruits table");
                stmt.executeUpdate();
            }
        }
    }

    protected static void populateDatabase() throws SQLException, IOException {
        removeAlFruits();
        insert("Apple", ImageIO.read(new File("Apple.png")));
        insert("Banana", ImageIO.read(new File("Banana.png")));
        insert("Cherries", ImageIO.read(new File("Cherries.png")));
        insert("Grapes", ImageIO.read(new File("Grapes.png")));
        insert("Orange", ImageIO.read(new File("Orange.png")));
        insert("Pear", ImageIO.read(new File("Pear.png")));
        insert("Pine Apple", ImageIO.read(new File("PineApple.png")));
        insert("Strewberry", ImageIO.read(new File("Strewberry.png")));
        insert("Water Melon", ImageIO.read(new File("WaterMelon.png")));
    }

    protected static void insert(String name, BufferedImage image) throws SQLException, IOException {
        String cmd = "insert into fruits (name, image) values (?, ?)";
        try (Connection con = makeConnection()) {
            try (PreparedStatement stmt = con.prepareStatement(cmd)) {
                try (InputStream is = convertImageToInputStream(image)) {
                    System.out.println("> Insert " + name);
                    stmt.setString(1, name);
                    stmt.setBinaryStream(2, is);
                    int rows = stmt.executeUpdate();
                    System.out.println("> " + rows + " rows updated");
                }
            }
        }
    }

    protected static InputStream convertImageToInputStream(BufferedImage image) throws IOException {
        ByteArrayOutputStream baos = null;
        ByteArrayInputStream bais = null;
        try {
            baos = new ByteArrayOutputStream();
            ImageIO.write(image, "png", baos);
            baos.close();
            bais = new ByteArrayInputStream(baos.toByteArray());
        } finally {
            if (baos != null) {
                try {
                    baos.close();
                } catch (IOException ex) {
                }
            }
        }
        return bais;
    }

    protected static void removeAlFruits() throws SQLException {
        String cmd = "delete from fruits";
        try (Connection con = makeConnection()) {
            try (PreparedStatement stmt = con.prepareStatement(cmd)) {
                System.out.println("> Remove all fruits");
                int rows = stmt.executeUpdate();
                System.out.println("> " + rows + " rows updated");
            }
        }
    }

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    try {
                        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                        ex.printStackTrace();
                    }

                    JFrame frame = new JFrame("Testing");
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.add(new TestPane());
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (SQLException | IOException ex) {
                    ex.printStackTrace();
                }
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() throws SQLException, IOException {
            setLayout(new BorderLayout());
            DefaultTableModel model = makeTableModel();
            JTable table = new JTable(model);
            table.setRowHeight(100);
            add(new JScrollPane(table));
        }

        protected DefaultTableModel makeTableModel() throws SQLException, IOException {
            DefaultTableModel model = new DefaultTableModel(new String[]{"Name", "Image"}, 0) {
                @Override
                public Class<?> getColumnClass(int columnIndex) {
                    return columnIndex == 1 ? Icon.class : super.getColumnClass(columnIndex);
                }

            };
            String cmd = "select name, image from fruits";
            try (Connection con = makeConnection()) {
                try (PreparedStatement stmt = con.prepareStatement(cmd)) {
                    try (ResultSet rs = stmt.executeQuery()) {
                        while (rs.next()) {
                            String name = rs.getString(1);
                            Blob blob = rs.getBlob(2);
                            ImageIcon icon = null;
                            try (InputStream is = blob.getBinaryStream()) {
                                BufferedImage img = ImageIO.read(is);
                                icon = new ImageIcon(img);
                            }
                            model.addRow(new Object[]{name, icon});
                        }
                    }
                }
            }
            return model;
        }

    }
}

替代方法是使用自定义 TableCellRender，如 Rendering BufferedImage in JTable cell

中所示

试图从 mysql 中检索文本和 blob 到 jtable

trying to retrieve both text and blob from mysql to jtable

java

swing

blob

jtable

tablecellrenderer

可运行示例...